docs: def ensure_session_key(request):
      """
      Given a request return a session key that will be used. There may already
      be a session key associated, but if there is not, we force the session to
      create itself and persist between requests for the client behind the given
      request.
      """
      key = request.session.session_key
      if key is None:
          # @@@ Django forces us to handle session key collision amongst
          # multiple processes (not handled)
          request.session.save()
          # force session to persist for client
          request.session.modified = True
          key = request.session.session_key
      return key